An etiology of nephrotic syndrome in chronic interstitial nephritis (pyelonephritis); an electron microscopic study.

Renal tissues were studied using electron microscopy (EM) and immunofluorescence microscopy (IFM) from three patients who were found to have chronic interstitial nephritis (pyelonephritis) by light microscopy (LM). By LM, 90% of the glomeruli in two patients and all glomeruli in one patient were normal. By EM, glomerular capillaries in all patients revealed generalized fusion of epithelial foot processes. In two patients, IFM for immunoglobulins, third component of complement and fibrinogen were negative. These two patients received corticosteroids for 6 to 12 weeks. In one, proteinuria markedly decreased (from 17.9 to 1.1 gm) in four weeks and in the other follow-up studies of renal histology revealed normal glomeruli and partial restoration of foot processes by LM and EM respectively. Thus, this study offers evidence for lipoid nephrosis (or minimal lesion disease) as an etiology of nephrotic syndrome in chronic interstitial nephritis (pyelonephritis). The impaired renal function in these patients is attributed to tubulo-interstitial disease rather than glomerular pathology. It remains to be determined whether the two disparate pathological conditions have coexisted or chronic interstitial nephritis had led to the appearance of lipoid nephrosis through an unidentified mechanism.